Controlling the underground spontaneous combustion of coal using an expansive aerosol

To efficiently and sustainably prevent the frequent occurrence of the spontaneous combustion of lignite in goaf areas, an expansive aerosol is proposed. Owing to the high expansion rate of expandable graphite (EG), phytic acid (PA) was employed for its modification, resulting in a PA-modified EG (PAEG) with enhanced performance. PAEG was combined with diatomite, silica, calcium hydroxide, fly ash, and magnesium hydroxide to formulate the expansive aerosol. The effects of varying doses of PA on EG were examined using scanning electron microscopy and thermogravimetric analysis. As the PA dose increased, the cross-linking of PAEG was enhanced and the residual mass increased after exposure to high temperatures (30-800 degrees C). Moreover, the volume expansion loss rate decreased from 97.32 % to 32.18 %, demonstrating the significant impact of the modification. Shanxi lignite was selected as the research object and treated with the fabricated expansive aerosol. The experimental and simulation data on the raw and aerosol-treated coal samples revealed a robust synergistic effect among the expansive aerosol materials, thereby significantly increasing the O2 absorption temperature, spontaneous combustion point, and activation energy. When the ratio of diatomite: silica: calcium hydroxide: fly ash: magnesium hydroxide: PAEG was 3:1:5:6:5:5, the O2 absorption temperature increased by 20.36 degrees C, spontaneous combustion point increased by 12.62 degrees C, and activation energy in thermal decomposition stages was 5.85 x higher than the raw coal sample. This study provides valuable insights for applying EG to prevent spontaneous coal combustion.